Real-life "water" arrows are possible, not with water (it weighs too much in an arrow tip), but with a modern class of fire-extinguishing chemicals.

Water has to hit the combustion zone of the fire, cooling it down and wetting it immediately, stopping combustion. Exact targeting is difficult, most water gets wasted by missing the critical combustion zone.

CO2 works by denying access of O2 to the combustion zone; it merely "suffocates" the reaction. This works well in closed systems, but not so well in open ones, because the CO2, being a gas, is quickly removed by any air current;

even absent any air currents (wind), CO2 is heavier than air and will quickly sink down; real-life torch-dousing arrows based on CO2 are therefore also impractical.

But another class of extremely efficient fire-extinguishing chemicals exists: Halons. These are small-molecule organic compounds, usually easily liquefiable gases, that have some of their hydrogen atoms replaced by halogens (fluorine, chlorine, bromine etc.). They have a low density, even in liquefied state (by keeping them in a pressurized vessel like a spray-can; generally an amount the size of a walnut would weigh little and contain more than enough of Halon to douse a torch, while on impact would be released in a gas-cloud form immediately due to being a pressure-liquefied gas).

Halons work wonders in stopping fires due to stopping the radical reaction that a fire is, basically - when the gas comes in contact with the hot combustion zone, the heat breaks up the Halon gas, making free radicals of halogens available, that react with the fire-supporting radicals that fuel the fire and stop the chain reaction of the chemical process that we call "fire".

The most relevant aspect of Halon gases is that only very little of it is effective in stopping fires; for many Halons, a concentration of just 0,1 % of it around the fire's combustion zone is enough to end the combustion immediately.

So, a real-life Garrett would use Halon arrows - they are practical and longer-ranged as well as precise because the effective amount to douse torches weighs very little and can be put in the tip of an arrow without ruining ballistic performance; on impact-release, the halon, due to being a pressure-liquefied gas, will automatically disperse itself in a gas cloud enshrouding the torch and dousing it at once silently without any suspicious remnants of deliberate action (--> stealth).

During the 80s, Germany considered Halons as an anti-tank rocket payload; because it is so effective in stopping and suppressing combustion even at very low concentrations, it can reliably stop and disable combustion engines even if only very little of it enters the air intake of a combustion-engine vehicle (no very precise aiming would be necessary to stop a tank, therefore).

"Good people do not need laws to tell them to act responsibly while bad people will find a way around the laws." - Plato"When outmatched... cheat."— Batman

-I don't know how hyperbolic is this "freezes all tissues and organs surrounding the point of injection on land or at sea" but for a sake of fiction it is good enough scientific explanation of freezing enemies with a missile.